1. Field of the Invention
The present invention relates in general to a seat reclining mechanism, and more particularly to a seat reclining mechanism for adjusting the angular position of a seatback relative to a seat cushion by a planetary gear arrangement.
2. Description of the Prior Art
Japanese Utility Model First Provisional Publication 3-847 discloses a seat reclining mechanism comprising a base plate, a pivotable arm, a rotatable shaft, a control gear, a plurality of planetary gears and a pair of supporting plates. Each supporting plate has three circular holes for receiving therein boss portions of the planetary gears. All the three circular holes are equidistantly spaced from the center of the supporting plate in a radial direction thereof. Each supporting plate is fitted into a cylindrical recess formed on the base plate or the pivotable arm in a manner that the supporting plate can rotate within the cylindrical recess. Thus, the supporting plate is positioned by fitting the supporting plate into the cylindrical recess. However, this seat reclining mechanism has the following drawbacks.
If play between the planetary gears and ring gears of the base plate and of the pivotable arm exceeds a certain allowable range, for example, it is necessary to replace the planetary gears by new ones which are larger in size. This increases the production cost. When the rotatable shaft is rotated, each planetary gear revolves on its axis and round the control gear. Due to this, each supporting plate is rotated on its own axis under the condition that a peripheral cylindrical surface of the supporting plate is in abutment with a cylindrical surface of the recess. Therefore, each supporting plate can not rotate smoothly and durability of the same is not satisfactory.